1. Field of the Invention
The present invention relates generally to a disk drive unit mounting an acceleration sensor and a control method for the disk drive unit, and more particularly, to a device and method for compensating for the effects of an external disturbance on a disk drive unit mounting one or more acceleration sensors.
2. Description of Related Art
Conventionally, in the field of magnetic disk drive units, the magnetic recording and/or readout (hereinafter recording and readout) of information to and from a rotating recording medium such as a magnetic or optical disk involves positioning the magnetic head appropriately with respect to the rotating disk so as to carry out optimum magnetic recording and readout.
In such cases, external disturbances imparted to the disk drive unit can affect the positioning of the magnetic head. In particular, the rotary-type actuator that is sometimes used as a magnetic head drive mechanism is particularly susceptible to external disturbances which coincide with a radial direction of the rotating disk (hereinafter referred to as a radial disturbance).
One method that has been proposed for correcting for the effects of such external disturbances on the positioning of the magnetic head with respect to the rotating disk involves mounting acceleration sensors on the magnetic disk drive unit frame or on top of the printed circuit board, sensing vibrations from external disturbances or from the reaction of the magnetic disk drive unit itself to a seek operation, and using the data so detected to correct for the effects of the vibrations. In particular, one method for sensing vibrations due to external disturbances in a radial direction of the rotating disk involves using a single acceleration sensor to detect directly the angular velocity imparted by the external disturbance.
The disadvantage of the above-described method is that the acceleration sensor is either expensive, has a low frequency response, or is relatively large.
In contrast to the above-described method, another, less expensive, method has been proposed in which two acceleration sensors are disposed along a single axis on the magnetic disk drive unit for sensing vibrations along the single axis (including the vibrational component of the external disturbance along such single axis), and processing the output of these acceleration sensors to obtain the effects of the external disturbance along both the single axis and the radial direction.
Examples of such conventional dual-sensor arrangements are shown in FIG. 1 and FIG. 2.
FIG. 1 is an abbreviated plan view of a printed circuit board portion of a conventional magnetic disk drive unit upon which two acceleration sensors are mounted. FIG. 2 is a diagram illustrating an operation of a conventional magnetic disk drive unit upon which acceleration sensors are mounted.
As shown in the diagrams, two acceleration sensors 1a, 1b are located at a right edge section of the circuit board 2, spaced a distance L apart. Servo information recorded on a magnetic disk 3 is read by a magnetic head 4. A servo signal read from the magnetic head 4 is amplified by a playback amplifier 5a and demodulated to position data by servo demodulation circuit 5b. The position data from the servo demodulation circuit 5b is then taken in by a microprocessor 6.
At the same time, data indicating detection of an disturbance by the acceleration sensors 1a, 1b (hereinafter referred to as disturbance data) is also taken in by the A/D converter 6a of the microprocessor 6.
The position data and disturbance data read in by the microprocessor 6 are then processed by a CPU 6c using a program recorded in a memory 6b in order to generate a control signal.
The control signal is then sent via a DA converter 6d to a VCM driver 7 in order to drive a voice coil motor (VCM) 8 so as to position the magnetic head 4, such position being corrected for the effects of the external disturbance.
In this case, the radial disturbance is obtained as angular acceleration xcfx89 (in units of rad/sec2). However, this angular acceleration xcfx89 is obtained from outputs G1, G2 (units: G) of the two acceleration sensors and the distance L (in meters) between the two acceleration sensors according to the following formula (where g is 9.8 m/sec2):
xcfx89=(G1xe2x88x92G2)g/L
FIG. 3 is a circuit diagram illustrating the operation of a magnetic disk drive unit mounting the conventional acceleration sensor.
As shown in the diagram, the disturbance data provided by the acceleration sensors 1a, 1b is then processed by the filter 9a and gain adjusted to get a correction signal Sb. By subtracting the correction signal Sb from an output signal Sa of a controller 9b of an ordinary feedback control system, a command value S that cancels the disturbance is imparted to a control object 9c. 
However, a disadvantage of the above-described conventional arrangement arises if there is a disparity in sensitivity between the two acceleration sensors when using the difference between the output values of the two acceleration sensors (which sense movement in a direction parallel to a surface of the disk) in order to obtain an amount of movement in a radial direction, because the vibration component in the direction parallel to the surface of the disk cannot be cancelled, thus producing incorrect radial disturbance data for the difference in detected values leading to improper disturbance correction.
Another disadvantage of the above-described conventional arrangement arises if there is a phase lag in the radial disturbance data detected by the acceleration sensors, which in turn leads to improper disturbance correction.
Accordingly, it is a general object of the present invention to provide an improved and useful disk drive unit control method and disk drive unit, in which the above-described disadvantages are eliminated.
The above-described object of the present invention is achieved by a control method for a disk drive unit upon which are mounted acceleration sensors, the control method comprising the step of changing a sequence for calculating an amount by which a head actuator is adjusted during recording and readout operations based on an output from the acceleration sensors.
According to the invention described above, adverse effects to the feedback system can be prevented when performing feed forward correction control of a radial disturbance.
Additionally, the above-described object of the present invention is achieved by a control method for a disk drive unit upon which are mounted two acceleration sensors positioned a predetermined distance apart, the control method comprising the step of changing a sequence for calculating an amount by which a head actuator is adjusted during recording and readout operations based on an output from the two acceleration sensors sensing parallel components of an external disturbance on the disk drive unit in a direction parallel to a surface of a disk.
It should be noted that the direction parallel to the surface of the disk is meant to include, but not be limited to, a radial direction of the disk to be described later, and, as such, constitutes a uniaxial direction. In the invention to be described below, in which acceleration sensors are positioned so as to sense acceleration in a same direction, this uniaxial direction is referred to as the parallel direction for ease of explanation, parallel in the sense that movement is in a direction parallel to a surface of the disk.
According to the invention described above, adverse effects to the feedback system can be prevented.
Additionally, the above-described object of the present invention is achieved by a disk drive unit upon which are mounted acceleration sensors, the disk drive unit comprising a correction control unit for changing a sequence for calculating an amount by which a head actuator is adjusted during recording and readout operations based on an output from the acceleration sensors.